Tackling a crossword can crowd the tip of your tongue. You know that you know the answers to 3 Down and 5 Across, but the words just won’t come out. Then, when you’ve given up and moved on to another clue, comes blessed relief. The elusive answer suddenly occurs to you, crystal clear.

The processes leading to that flash of insight can illuminate many of the mind’s curious characteristics. Crosswords can reflect the nature of intuition, hint at the way we retrieve words from our memory and reveal a surprising connection between puzzle-solving and our ability to recognize a human face.

“What’s fascinating about a crossword is that it involves many aspects of cognition that we normally study piecemeal, such as memory search and problem-solving, all rolled into one ball,” says Raymond Nickerson, a psychologist at Tufts University. In a paper published last year, he analyzed the mental processes of crossword-solving.

Pre-consciousness

Most of our mental machinations take place subconsciously, or pre-consciously, with the results dropping into our conscious minds only after the answers to clues have been decided elsewhere.

At other times, you might need to take a more methodical approach and consider possible solutions one by one, perhaps listing synonyms of a word in the clue.

Even if your list doesn’t seem to make much sense, it might reflect the way your pre-conscious mind is homing in on a solution. Nickerson points to work in the 1990s by Peter Farvolden at the University of Toronto, who gave his subjects four-letter fragments of seven-letter target words. While his volunteers attempted to work out the target, they were asked to give any other word that occurred to them in the meantime. The words tended to be associated in meaning with the eventual answer, hinting that the pre-conscious mind solves a problem in steps.

Should your powers of deduction fail you, it may help to let your mind chew over the clue while your conscious attention is elsewhere. Studies back up our everyday experience that a period of incubation can lead you to the eventual “aha” moment. Don’t switch off entirely, though. For verbal problems, a break from the clue seems to be more fruitful if you occupy yourself with another task, such as drawing a picture or reading.

Thinking out loud

Pre-conscious processing is hidden from us, so it is not clear how the mind sifts through things to answer a clue. Because written language is only a recent reflection of the long-evolved spoken word, Nickerson suspects that sounds are important. He illustrates this with a simple puzzle: Quickly think of four-letter words ending in -any, -iny, -ony, -uny and -eny. (When you’ve done it, read on.)

You probably had little trouble with the first four but may have struggled with the last one. Nickerson thinks that is because the only common four-letter word ending in -eny (deny)has a different pattern of stress from the natural way of reading the three-letter fragment. Research supports this idea, showing that a three-letter syllable forms a more effective clue than three other consecutive letters. So our mental dictionary is not just alphabetical but also phonological. In which case, it may help to say the clue or your guesses out loud.

Tip of the tongue

When solving these puzzles, you might initially have a strong feeling about whether you know the answer — and these sentiments are likely to be right. Given a mixture of solvable and unsolvable word-association tests, subjects tend to guess correctly which ones they will and won’t be able to answer. In crosswords, says Nickerson, this “feeling of knowing” can be useful. If you are pretty sure you know the answer, you sensibly spend more time trying to get it; if you are certain that you don’t, you move on and try to get intersecting words instead.

Psychologists make a fine distinction between this feeling of knowing and a sense of something being “on the tip of the tongue.” The latter, more irritating state is the feeling that an answer will come soon, rather than that it will come eventually. It is often false, as the phantom of revelation fades away. One theory is that a wrong word retrieved from our memory blocks the way for the right word, an occurrence that Nickerson recognizes in crossword-solving when an initial wrong guess makes it more difficult to find the true solution.

Double-think

Be careful with the more difficult puzzles: Cryptic crosswords can warp the mind in surprising ways. Michael Lewis of Cardiff University in the United Kingdon came to this conclusion while investigating why results from police lineups are so unreliable. He was following up research showing that face recognition can become temporarily impaired after a person is shown a large alphabetical letter made up of a configuration of smaller, different letters and is asked to read out the smaller letters while ignoring the larger one. This seemingly innocuous preparation, known as a local Navon task, made them much worse at a face recognition test.

Nobody is likely to perform a Navon task before being asked to pick out someone in a lineup, so Lewis looked at more common waiting-room activities: sudoku puzzles, reading a book, literal crosswords and cryptic crosswords. (Cryptic crosswords typically have clues that, when they are read literally, have nothing to do with the answer; each clue must be split into two parts, each of which leads separately toward the answer.) Lewis thought the sudoku puzzles would have the biggest effect; he included the crosswords only as controls. But the subjects tackling the first three types of tasks all achieved roughly the same results in face recognition tests, whereas those wrestling with cryptic clues performed far worse.

Lewis speculates that some form of suppression may play a role. In the Navon task, you must suppress the global picture, and in cryptic crosswords it helps to suppress larger linguistic units and break up phrases to look for hidden wordplay and definitions. As a side effect, that seems to suppress our ability to see a face as a whole unit. The phenomenon goes beyond visual and verbal realms: Navon stimuli also affect wine-tasting ability, says Lewis. “It suggests there is some overlap in processing between all these tasks.”

Crosswords naturally probe connections between ideas and words, and Nickerson suggests that psychologists could make more use of these puzzles when studying cognition. The human mind is itself a fiendish puzzle, so perhaps it’s not surprising that crosswords cast light on its workings.

Comments our editors find particularly useful or relevant are displayed in Top Comments, as are comments by users with these badges: . Replies to those posts appear here, as well as posts by staff writers.

To pause and restart automatic updates, click "Live" or "Paused". If paused, you'll be notified of the number of additional comments that have come in.

Comments our editors find particularly useful or relevant are displayed in Top Comments, as are comments by users with these badges: . Replies to those posts appear here, as well as posts by staff writers.